The present invention relates to a non-reciprocal circuit element used for a millimeter-wave hybrid integrated circuit board provided with an active element such as a semiconductor element mounted thereon, and a millimeter-wave hybrid integrated circuit board with the non-reciprocal circuit element.
In an active element mounted on a circuit such as a millimeter-wave circuit, transmitting radio wave having an extremely short wavelength, the following problems have occurred.
(1) Since a line length of the circuit is too long to be ignored relative to the wavelength, the reflection from the active element may produce a standing wave in the line causing change in the load impedance depending upon the frequency to easily occur; and
(2) since a reverse-direction transfer coefficient cannot be reduced due to an existing inner capacitance of the active element, a back-flow of signals may extremely increase to cause an unstable phenomenon such as oscillation and runaway of the circuit or a large variation in a frequency characteristics of the circuit.
In order to solve such the problems, it is very effective to insert a non-reciprocal circuit element such as an isolator between active elements so as to reduce the standing wave.
A monolithic millimeter-wave integrated circuit has been demanded as a future semiconductor integrated circuit operating at a millimeter-wave range. However, because a current semiconductor element for a millimeter-wave range has a low manufacturing yield, mass production is quite difficult for a monolithic millimeter-wave integrated circuit. Therefore, in order to solve the yield problem, it is most effective to fabricate a millimeter-wave hybrid integrated circuit with a dielectric board. For a stable operation of such hybrid integrated circuit, a millimeter-wave isolator acts as an extremely important circuit element.
The operation of the millimeter-wave isolator requires a strong magnetic field. Namely, a typical circulator used at a microwave band or a higher-wave band called as a distributed element circulator consists of a TM110 resonator with a magnetized ferrite body. A magnetic field to be applied to the ferrite body increases with the increase in frequency, and thus in the millimeter-wave band, a strong magnetic field of 5000 Oe or more is required. A conventional millimeter-wave isolator obtains such a strong magnetic field from an externally mounted magnetic circuit with an extremely large size. Therefore, it is hardly possible to mount the conventional millimeter-wave isolator and the magnetic circuit onto a millimeter-wave hybrid integrated circuit.
It is therefore an object of the present invention to provide a non-reciprocal circuit element which can be easily mounted onto a millimeter-wave hybrid integrated circuit board, and a millimeter-wave hybrid integrated circuit board with the non-reciprocal circuit element.
The present invention is intended (1) to mount a non-reciprocal circuit element such as an isolator on a millimeter-wave hybrid integrated circuit board so as to eliminate a wave reflected into the board, thereby stabilizing the circuit operation, and (2) to form a pattern, on the millimeter-wave hybrid integrated circuit board, for providing a non-reciprocal circuit element only by mounting a spontaneously magnetized ferrite body thereon as well as done in an ordinary component mounting process.
According to the present invention, a non-reciprocal circuit element includes a microstrip TMn10 resonator (n is a positive integer) with a metal disk and branches projecting from the metal disk in a trigonally symmetric structure, and a ferrite magnetic body spontaneously magnetized and coaxially disposed on the microstrip TMn10 resonator. The metal disk and the branches are formed on a non-magnetic dielectric board having a ground conductor on its bottom face. The ferrite magnetic body is arranged so that a position of an electric field node matches to one of the branches. Thus, the non-reciprocal circuit element can be easily mounted onto a millimeter-wave hybrid integrated circuit board.
In other words, according to the present invention, trigonally symmetric branches are provided between lines connecting integrated circuits on a millimeter-wave hybrid integrated circuit board that is constituted by a non-magnetic dielectric board and provided with a ground conductor on its back surface to form a TMn10 resonator (n is a positive integer), and a magnetic body is disposed thereon to form a circulator. Additionally, a spontaneously magnetized ferrite magnetic body is used as the magnetic body eliminating the need for an external magnetic circuit. The ferrite magnetic body is magnetized and dimensioned such that a position of an electric field node matches to one of the branches (a third terminal not connected to the integrated circuit). If this third terminal is terminated by a matching resistor, an isolator is formed.
If a reflected wave between integrated circuits is absorbed by such a non-reciprocal circuit element, load impedance on a signal-transmitting side becomes constant regardless of input impedance on a signal-receiving side. Hence, it is possible to prevent problems such as oscillation and runaway of a power amplifier that are caused by the reflected wave in the circuit. Particularly in case of a millimeter wave band amplifier, since an increase in reverse-direction transfer constant of a transistor due to inner capacitance of the element cannot be ignored, it is quite important to make a signal to be directional in order to operate a circuit with stability.
Preferably the ferrite magnetic body has a shape of a disk or a cylinder.
It is preferred that the TMn10 resonator is a TMn10 resonator, where m is a positive integer of 2 or more. In this case, it is preferable to partially remove a portion of the metal disk around a central axis or a portion of the ferrite magnetic body and metal disk around the central axis. This arrangement makes it possible to reduce TM010 mode, which is a resonance frequency of the TM010 resonator, appearing in a resonance frequency band of the TMm10 resonator.
As a modification, it is preferable to metallize an inner wall of a hole formed in the ferrite magnetic body by removing a portion around a central axis. Thus, the TM010 mode can be suppressed more effectively.
It is also preferable to metallize at least the top and bottom faces of the ferrite magnetic body. Hence, it is possible to increase a magnetic flux appearing in the ferrite magnetic body.
It is also preferred that the TMn10 resonator is a TM110 resonator, and that a Faraday rotator with a ferrite cylinder that has a metallized free end face and a propagation length of one wavelength. As for a modification in this case, preferably a non-magnetic dielectric body is coupled to the ferrite cylinder.
It is preferred that a dielectric constant of the non-magnetic dielectric body is selected such that the ferrite cylinder and the non-magnetic dielectric body are equal to each other in characteristic impedance. This arrangement makes it possible to suppress reflection on a coupling surface between the ferrite cylinder and the non-magnetic dielectric body.
Preferably, xc2xc wavelength impedance matching elements are connected to the branches, respectively. This arrangement makes it possible to widen an operational frequency band.
It is preferred that one terminal is connected to a matching resistor and other two terminals are formed as input and output terminals.
It is also preferred that the dielectric board is a millimeter-wave hybrid integrated circuit board.
According to the present invention, furthermore, a millimeter-wave hybrid integrated circuit board has at least one non-reciprocal circuit element mentioned above.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.